This paper describes with the dispersion of arc spots caused by the material of the tool electrode. In the EDM it is well known that only one crater of the arc spot at the surface of the electrode is formed due to a single impulse discharge. In this experiment several arc spots are easily formed by using the electrode of the resistance material and conductive material with a special shape in view of the internal resistance. These unique phenomena are explained by means of the internal resistance of the tool electrode. Several arc column are formed in parallel at the electrode gap by the cause of the internal resistance. The feature of the streak camera photograph shows the observation of the parallel arc column. This paper introduces these phenomena into one methode of improving the removal rate in the EDM.
